The current research on one of the hallmarks of alcohol's many actions, it's frequent biphasic effect. Low doses often produce activation of behavioral and physiological characters. The behavioral activation is variously described as a stimulant effect, euphoria, and disinhibition. Although clear resolution of dimensions is not yet available, such activating effects are now receiving focus in some genetically based theories of alcoholism, such as Cloninger's scheme of alcoholic subtypes. Type II is argued to use alcohol for these euphoriant effects, implying a genetically based sensitivity to this domain of ethanol action. Laboratory studies of behavioral activation by ethanol have shown clear genetic influences on this type of initial sensitivity. Mouse locomotor activity has been the most highly investigated phenotype for this question of ethanol activation. Data collected have already provided a convincing picture of the genetic control as a simple genetic system of a small polygenic size. Three congenic strains are being developed to facilitate studies of psychopharmacological, physiological, neurochemical, molecular genetic and other phenomenological aspects of ethanol's paradoxical low-dose stimulant-like effect. These congenic strains are three pairs of inbred strains which differ from the pair member at only those genes which control the behavioral activation phenotype (as well as a small amount of tightly linked DNA). The successful completion of their development, at generation 12, will produce tools with considerable value in studies of biological pleiotropisms of these genes, their physiological/biochemical functioning, and their molecular genetic location and identity. The coherence sensitivity to ethanol, its activational effects.